The document discusses the functions and structures of the air bladder and Weberian ossicles in bony fishes, explaining their roles in buoyancy regulation, hydrostatics, and sound production. It outlines the basic structure, types of swim bladders (physostomous, physoclistous, and transitional), and their functionality in respiration and equilibrium within water. The Weberian ossicles enhance sound transmission to the inner ear and are sensitive to changes in swim-bladder volume, acting as pressure registers and auditory organs.

1. AIR BLADDER-FUNCTIONS
&
WEBERIAN OSSICLES
BY,
SWATHILAKSHMI PS
OST-2021-20-26

2. WHAT IS AIR BLADDER?
• An air filled sac
• Lying above the alimentary canal in bony fishes
• That regulates buoyancy at different depth by a variation in the
pressure of the air

4. ROLE OF SWIM BLADDER
• In most of the fishes a characteristic sac-like structure is present
between the gut and the kidneys.
• The swim-bladder occupies the same position as the lungs of higher
vertebrates and is regarded as homologous to the lungs.
• It differs from the lungs of higher forms mainly in origin and blood
supply.
• The swim-bladder arises from the dorsal wall of the gut and gets the
blood supply usually from the dorsal aorta, while the vertebrate lung
originates from the ventral wall of the pharynx and receives blood
from the sixth aortic arch.
• The swim-bladder is present in almost all the bony fishes and
functions usually as a hydrostatic organ

5. DEVELOPMENT OF AIR BLADDER
• In teleost-unpaired dorsal or dorso lateral diverticulam of the
oesophagus
• Start as small pouch budded –off from the oesophagus
• Subsequently divided in 2 halves
• In dipnoans & polypteride, the swim bladder is modified into lungs

6. BASIC STRUCTURE OF AIR BLADDER
• The swim bladder in fishes varies greatly in structure ,size and shape
• Its essentially a trough like structure with an overlying capillary network
• Beneath the capillary system the wall of the anterior part of swim bladder
consist of the following
(a)Tunica externa
(b)Sub mucosa
(c)Muscularis mucosa
(d)Lamina propria
(e)Innermost layer

7. • In posterior chamber of swim bladder , outside the layer of muscular
mucosa there is a glandular layer
• The swim bladder is open into the oesophagus , by a ductus
pneumaticus , which is short and wide in lower teolest
• The gas secreted by the swim bladder is mostly oxygen and little
amount of nitrogen and carbon dioxide are also present

8. TYPES OF SWIM BLADDER
(1)Physostomous condition
 The swim bladder devolps from the oesophagus
When the ductus pneumaticus is present between the swim bladder and the
oesophagus - physostomous type
This condition is observed in bony fishes , the diponoans and soft rayed fishes
(2)Physoclitous condition
In this condition the ductus pneumaticus is either closed or atrophied
This type of swim bladder is observed in spiny-rayed fishes
In this air bladder ,there lies an anteroventral secretory gas gland & a
posterodorsal gas absorbing region called the ovale

10. (c)Transitional condition
In Eel , a transitional condition between the physostomous and
physoclistous type is present
The swim bladder retains the ductus pneumaticus which become
enlarged to form a separate chamber containing the ovale

11. FUNCTION OF SWIM BLADDER
(a)Hydrostatic organ
• It is primarily a hydrostatic organ and helps to keep the weight of the
body equal to the volume of the water the fish displaces
• It also serves to equilibrate the body in relation to the surrounding
medium by increasing or decreasing the volume of gas content.
• In the physostomous fishes the expulsion of the gas from the swim-
bladder occurs through the ductus pneumaticus, but in the
physoclistous fishes — where the ductus pneumaticus is absent —the
superfluous gas is removed by diffusion.

12. (b)Adjustable float
The swim-bladder also acts as an adjustable float to enable the fishes
to swim at any depth with the least effort. When a fish likes to sink, the
specific gravity of the body is increased. When it ascends the swim-
bladder is distended and the specific gravity is diminished. By such
adjustment, a fish can maintain an equilibrium at any level.

13. (c)Maintain proper center of gravity:
The swim-bladder helps to maintain the proper center of gravity by
shifting the contained gas from one part of it to the other and thus
facilitates in exhibiting a variety of movement.

14. (d)Respiration:
The respiratory function of the swim-bladder is quite significant. In
many fishes living in water in which oxygen content is considerably low,
the oxygen produced in the bladder may serve as a source of oxygen. In
few fishes, specially in the dipnoans, the swim-bladder becomes
modified into the ‘lung’. The ‘lung’ is capable of taking atmospheric air.

15. (e)Resonator:
The swim-bladder is regarded to act as a resonator. It intensifies the
vibrations of sound and transmits these to the ear through the
Weberian ossicles.

16. (f)Production of sound:
• Many fishes, Doras, Platystoma, Malapterurus, Trigla can produce grunting
or hissing or drumming sound. The circulation of the contained air inside
the swim-bladder causes the vibration of the incomplete septa. The sound
is produced as the consequence of vibration of the incomplete septa
present on the inner wall of the swim- bladder.
• The vibrations are caused by the movement of the contained air of the
swim- bladder. Sound may also be produced by the compression of the
extrinsic and intrinsic musculatures of the swim-bladder. Polypterus,
Protopterus and Lepidosiren can produce sound by compression and
forceful expulsion of the contained gas in the swim-bladder.

17. WEBERIAN OSSICLES
• The Weberian apparatus is named after the German anatomist and
physiologist ERNST HEINRICH WEBER(1795 – 1878). The apparatus was
first described in detail by Weber
• The perilymphatic sac and the anterior end of the swim-bladder are
connected by a series of four ossicles which are articulated as a conducting
chain.
• Of the four, the tripus, intercalarium and scaphium actually form the chain,
while the fourth one, claustrum lies dorsal to the scaphium and lies in the
wall of posterior prolongation of the perilymphatic sac.
• the Weberian ossicles either help to intensify sound vibrations and convey
these waves to the internal ear, which help to understand the state of
tension of air pressure in the bladder and transit changes of such pressure
to the perilymph to set up a reflex action.

19. Functions of the Weberian Ossicles
1. As pressure register:
• They are sensitive to changes in the volume of the swim-bladder due
to variations in the hydrostatic pressure. Any change in the volume of
the swim-bladder causes movements of the sinus impar. This is then
conveyed to the sacculus through the endolymph of the transverse
canal.

20. 2. As barometer:
• It is presumed that fish can detect variation in the atmospheric pressure
through Weberian ossicles.
3. As auditory organ:
• The ossicles transmit the vibrations of the bladder wall to the perilymph of
sinus impar. The vibration reach the saccular otoliths via endolymph.
4. As sound locator:
• The vibrations received on the side of the bladder nearest the source are
stronger than the other side.

21. THANKYOU